Inspector Lestrade of Scotland Yard brings Holmes a seemingly trivial problem about a man who shatters plaster busts of Napoleon I (the Emperor of France who led France in the French-European War (1789-1815)). One was shattered in Morse Hudson’s shop, and two others, sold by Hudson to a Dr Barnicot, were smashed after the doctor’s house and branch office had been burgled. Nothing else was taken. In the former case, the bust was taken outside before being broken.

Holmes knows that Lestrade’s theory about a Napoleon-hating lunatic must be wrong. The busts in question all came from the same mould. Why is he breaking them?
The next day, Lestrade calls Holmes to a house where there has been yet another bust-shattering, but there has also been a murder. Mr Horace Harker found the dead man on his doorstep after investigating a noise. His Napoleon bust was also taken by a burglar entering through a window. It, too, was from the same mould. Also, a photograph of a rather apish-looking man is found in the dead man’s pocket.

The fragments of Harker's bust are in the front garden of an empty house up the street. Obviously the burglar wanted to see what he was doing, for there is a streetlamp here, whereas the bust could have been broken at another empty house nearer Harker’s, but it had been dark there.
Holmes tells Lestrade to tell Harker, a journalist for the Central Press Syndicate, that he is convinced that the culprit is a lunatic. Holmes knows that this is not true, but it is expedient to use the press to convince the culprit that this is what the investigators believe.

Holmes interviews the two shopkeepers who sold the busts and finds out whom they were sold to, and where they were made, Gelder & Co. A couple of his informants also recognize the apish man in the picture. They know him as Beppo, an Italian immigrant. He even worked in the shop where the first bust was broken, having left his job there only two days earlier.

Holmes goes to Gelder & Co. and finds out that the busts were part of a batch of six, but other than that, the manager can think of no reason why they should be special, or why anyone would want to destroy them. He recognizes Beppo’s picture, and describes him as a rascal. He was imprisoned for a street-fight stabbing a year earlier, but has likely been released now. He once worked at Gelder & Co., but has not been back. His cousin still works there. Holmes begs the manager not to talk to the cousin about Beppo.

That evening, Lestrade brings news that the dead man has been identified as Pietro Venucci, a Mafioso. Lestrade believes that Venucci was sent to kill Beppo, but wound up dead himself. Why is the Mafia after Beppo?

After sending an express message, Holmes invites Dr Watson and Lestrade to join him outside a house in Chiswick where apparently Holmes is expecting another bust-breaking. Lestrade by now is exasperated with Holmes’s preoccupation with the busts, but comes. They are not disappointed. Beppo shows up, enters the house, and comes back out of the window minutes later with a Napoleon bust, which he proceeds to shatter. He then examines the pieces, quite unaware that Holmes and Lestrade are sneaking up behind him. They pounce, and Beppo is arrested. He will not talk, however.

The mystery is at last laid bare after Holmes offers £10 to the owner of the last existing bust, making him sign a document transferring all rights and ownership of the bust to Holmes. After the seller has left, Holmes smashes the bust and among the plaster shards is a gem, the black pearl of the Borgias. Holmes was aware of the case of its disappearance from the beginning. Suspicion had fallen on the owner’s maid, whose name was Lucretia Venucci – the dead man’s sister. Beppo somehow got the pearl from Pietro Venucci, and hid it inside a still-soft plaster bust at the factory where he worked, moments before his arrest for the street-fight stabbing.

After serving his one-year sentence, he sought to retrieve the hidden pearl. He found out from his cousin who bought the busts, and through his own efforts and confederates’, even found out who the end buyers were. He then proceeded to seek the busts out, smashing them one by one to find the pearl.
Although he appears in later published works, this is one of Lestrade's last appearances within the canon. After this he is only mentioned by Holmes or Watson, in "The Disappearance of Lady Frances Carfax" and "The Adventure of the Three Garridebs" as a working member of the Yard.

Napoleon is a man frequently mentioned in Sherlock Holmes-related work. In this story, someone smashes six busts of Napoleon. In the Grenada TV version of The Final Problem, Holmes visits the Louvre museum in Paris, where Napoleon Bonaparte was married to the Archduchess Marie-Louise of Austria. Holmes refers to Professor Moriarty as "the Napoleon of crime" and to Charles Augustus Magnussen as "the Napoleon of blackmail". Also mentioned is Trafalgar Square, built in tribute of Bonaparte's arch-enemy, Admiral Lord Horatio Nelson.